It is a fact that throughout the history of fish keeping there has always been a possibility that the introduction of new fish to an existing pond may mean the introduction of a disease or parasite infection. This is not a foregone conclusion as many new fish have been introduced to koi collections without any problems what-so-ever. Therefore purpose of quarantining is to protect your collection.


Let the Buyer Beware.

Koi keepers should always check the ponds where they intend to purchase from. Any dead koi, signs of stress, koi lying on the bottom, gulping at the surface etc should be viewed with suspicion.

Once you have made the purchase and taken delivery NEVER take for granted that the fish you purchase from ANY source are perfectly healthy. This is not pointing a finger but simple common sense to protect the most important person in koi keeping - you. Protect yourself - quarantine your own fish, if possible.

Protect Your Collection

The most effective way to protect a valuable collection is to prevent the introduction of diseases. NO fish should be added to a collection unless they have been adequately quarantined by you, the koi keeper. You must be reasonably sure the new purchases are not carrying any diseases and/or parasites. They should also be quarantined to allow them to rebuild their strength and immunity. This quarantining period does not have any fixed time, but should be a minimum of a few weeks.

Stressed, weakened koi will, in most cases, be open to attack from micro-organisms (e.g. bacteria and fungus) and macro-organisms (e.g. parasites). Therefore, as a precaution koi should be disinfected before adding to a collection.


EVERY koi you purchase must be viewed as a potential carrier of disease simply because ALL koi carry pathogens (pathogen = something which causes a disease) and some parasites.

Stress plays a major role in triggering diseases. The 'passengers' start multiplying. If the koi is weakened by stress it will not usually be able to cope with this increase in parasites and/or bacteria and an infection will result.


Biological Equilibrium

Koi, like all creatures, develop a specific immunity against the pathological agents (bacteria, fungal or other micro-organisms that will harm them) in its own pond. In other words the koi become accustomed to them. When this happens equilibrium is established. To put it another way, there is a mutual agreement between the koi and the organisms that live on it and around it in a common environment. Just as there is a mutual understanding between our bodies and the micro-organisms that live on us. We are very dependent on these friendly creatures, but, if our resistance is lowered for some reason the friendly 'bugs' can explode with a resulting infection.


Introducing New Koi

When new koi from other regions or other ponds are introduced, they bring in micro-organisms which they themselves have become immune to, but they may not be immune to the bacteria already present in the water or on your koi. The koi in your present collection may, in turn, not be immune to the new bacteria brought in with the new koi.

For example different strains of Aeromonas bacteria can cause cross infections. Koi A has become immune to bacteria type "a" that has developed in its own pond or dam. Koi B has become immune to bacteria type "b" in another pond or dam. If we place them together, bacteria type "b" infects koi A and naturally bacteria "a" infects koi B. In other words the equilibrium is broken and if the bacteria is a virulent strain that your fish are not immune to, an infection can be result.

You must Quarantine

It is not important whether the koi are moved from Japan to South Africa or moved from Johannesburg to Durban or even moved a few kilometers down the road. When you receive them, it is preferable that YOU must quarantine your new koi and observe them.

Fortunately, in most cases there will not be a problem. But, be prepared and observe the new fish regularly. When you are sure they are healthy you can introduce them to your present collection.


Direct Introduction of Koi into the Pond

There are many instances of people buying fish that have never been quarantined and introducing them directly into their ponds without any disease being spread. These koi keepers don't believe in quarantining their new koi because they believe that it will involve moving the fish twice and therefore, involve more stress.

The facts are you may be lucky and you may not be lucky.

If koi are quarantined for any length of time it stands to reason that those fish in the quarantine tank develop their own biological balance and eco system. The longer the quarantining period the more chance of this happening.